Environmental control systems for vehicles traditionally include a refrigeration system using a belt-driven compressor which is driven from the vehicle's engine at a speed that is determined by the engine speed. The compressor is cycled on and off in order to regulate the temperature of the air supplied to the passenger compartment. Such a system presents wide fluctuations in compartment temperature and is extremely inefficient in performance. Furthermore, the use of a belt-driven compressor results in significant leakage of environmentally damaging refrigerants to the atmosphere.
In order to overcome certain of these deficiencies, compressors having a variable output have been proposed with the output matched with the demand for cooling of the passenger compartment. Such systems may include wobble-plate compressors and variable speed electric-motor-driven compressors. While the latter may be supplied in a hermetically sealed unit, and hence reduce the level of refrigerant discharge to the atmosphere, both systems are less than optimum in meeting the goal of control cycle efficiency.
Another problem with known environmental control systems is that the saturation pressure of the refrigerant, especially within the condenser, is very high. In addition to presenting a safety hazard, such pressures dictate increased structural measures in the components of the system, which does not add to the overall performance of the system.